I usually stabilize the quilt by stitching in-the-ditch around the outer borders first. Then I stabilize half way between the outside and middle. Then things are pretty stable for the rest of the quilting. I'll do all of the stitch-in-the-ditch before adding free-motion or ruler work.
I do like to spray baste. But you've absolutely got to baste the raw edges together around the outside for the spray baste to hold. I do add some safety pins if the quilt is bigger than 45" square.